This adds a new method, partial_dependency to all dependencies. These
sub dependencies are copies of the original dependency, but with one or
more of the attributes replaced with an empty list. This allows creating
a sub dependency that has only cflags or drops link_arguments, for
example.
With the headers from cygwin-devel-2.10.0-1, getpagesize() is not prototyped
unless an appropriate feature test macro is defined.
Future work: investigate if this needs to be defined by
BoostDependency.get_compile_args() or in Boost.
Also, use '^' to escape newlines in appveyor-install.bat to avoid an
absurdly long line, remove some unnecessary quotation, and alphabetically
sort packages
Also, define the _XOPEN_SOURCE feature test macro in the boost test to avoid
'not declared in this scope' warnings for pthread_rwlock_init(), etc.
The new implementation will correctly pick boost from 3 possible
locations on windows and two locations on posix compatible OSs.
The new search algorithm also differentiates between debug and
release builds of Boost and multi or single threading builds.
It was also decided to map "Meson modules" to Boost software libraries
and not Boost modules since it there are a lot of options regarding
linking. Some modules can even be used either as headers-only or with
dynamic linking.
This commit also fixes a bug that prevented header-only use on Windows.
Fixes: #2274#2239#1803#669
Nicole Mazzuca
Jon Turney
Dylan Baker
Niklas Claesson
Michał Wikliński
Jussi Pakkanen
Adam C. Foltzer